Epitaxial and polycrystalline growth of Si1-x-yGexCy and Si1-yCy alloy layers on Si by UHV-CVD

ABSTRACT

A method and apparatus for depositing single crystal, epitaxial films of silicon carbon and silicon germanium carbon on a plurality of substrates in a hot wall, isothermal UHV-CVD system is described. In particular, a multiple wafer low temperature growth technique in the range from 350° C. to 750° C. is described for incorporating carbon epitaxially in Si and SiGe films with very abrupt and well defined junctions, but without any associated oxygen background contamination. Preferably, these epitaxial SiC and SiGeC films are in-situ doped p- or n-type and with the presence of low concentration of carbon &lt;10 20  cm −3 , the as-grown p- or n-type dopant profile can withstand furnace anneals to temperatures of 850° C. and rapid thermal anneal temperatures to 1000° C.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.10/775,514 filed Feb. 10, 2004, which is a divisional of U.S.application Ser. No. 09/838,892, filed Apr. 20, 2001, which is now U.S.Pat. No. 6,750,119.

Cross-reference is made to U.S. patent application Ser. No. 09/774,126filed Jan. 30, 2001, which is now U.S. Pat. No. 6,426,265 by Chu et al.entitled “Incorporation of Carbon in Silicon/Silicon Germanium epitaxiallayer to Enhance Yield for Si—Ge bipolar technology” which is directedto a method of fabricating a SiGe bipolar transistor including carbon inthe collector region as well as the SiGe base region and which isassigned to the assignee herein and incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to silicon-carbon and silicon germanium-carbonbased materials system and more specifically, to a novel method andapparatus for depositing single crystal and poly crystalline layers ofsilicon-carbon (Si:C) and silicon germanium-carbon (SiGe:C) on aplurality of substrates at low temperatures and low pressures. Amultiple wafer, low temperature growth technique is described forincorporating carbon epitaxially into Si and SiGe with very abrupt andwell defined junctions, without any associated oxygen backgroundcontamination. Preferably, these silicon carbon alloy films are devicequality, epitaxial layers which can be in-situ doped p- or n-type. Anarrow base p-type device structure may be fabricated incorporatingsilicon-carbon and silicon germnanium-carbon layers to form the baseregion of a high speed heterojunction bipolar transistor (HBT). Theincorporation of a low concentration of carbon<10²⁰ atoms cm⁻³ into theSiGe base region of a HBT can suppress boron outdiffusion and allow theuse of high boron doping levels (>>10¹⁹ cm⁻³) in a very thin SiGe basebase region (<20 nm) without suffering the effects of boron outdiffusionfrom post-epitaxial thermal processing and anneals.

BACKGROUND OF THE INVENTION

The next generation of SiGe HBTs suitable for wireless telecommunicationsystems, which operate at radio or microwave frequencies will bedesigned and targeted for very high speed SiGe bipolar devices havingf_(T) and f_(max) of over 100 GHz. Presently, state of the art SiGe-baseheterojunction bipolar transistors (HBT's) employ a graded SiGestructure to introduce an accelerating field across the base region inorder to achieve high frequency performance from 45 to 90 GHz. Hence, toachieve SiGe bipolar devices with f_(T) and f_(max) of over 100 GHz,another device enhancement or improvement will be required for thepresent graded SiGe based transistors. One possibility for performanceenhancement is the scaling of the base width of the device, which isvery difficult to achieve in manufacturing due to punch through of thebase region. The key difficulty associated with base width scaling is incontrolling the corresponding increase of the base doping to a highdoping concentration to avoid punch through, which is very difficult toachieve in manufacturing. The effect of the base thickness on the highfrequency performance of SiGe HBTs has been reported in a publication byE. Kasper et. al. entitled “Growth of 100 GHz SiGe-HeterobipolarTransistor (HBT) Structures”, Jpn. J. Appl. Phys. Vol. 33 Pt. 1, No. 4B,April 1994, pp. 2415-2418 which is incorporated herein by reference. Thereference showed a steady increase of f_(T) with the decreasing of theSiGe-base thicknesses. For example, starting with HBT's with a 65 nmbase thickness which did not exceed 20 GHz, transistors with a thinner40 nm base width had yielded 37-52 GHz, while devices with even thinner28-30 nm bases had exhibited even higher f_(T) in the range of 58-91GHz. Moreover, when the effective base thickness was further scaled downbelow 50% to a 25 nm or 22 nm base thickness an extremely high f_(T) of95-100 GHz was achieved corresponding to an increase of 4-5 times inf_(T) and demonstrating the influence of base thickness on the speed ofthe bipolar transistor. However, it is important to note that in thesevery narrow base SiGe transistors the base doping concentration was inthe extremely high range of about 8×10¹⁹ boron/cm³ which is necessary inorder to maintain a base sheet resistance of about 1.2 K-Ohm in such athin 20 nm base region without punchthrough.

Subsequently, in order to combine and benefit from both these criticaldevice enhancements for high speed performances in the present SiGe npnbipolar transistors, very high Ge content and more importantly very highboron doping concentration will be required in a thinner base region toachieve lower base sheet resistance and higher f_(max) transistorperformance. A heavily doped SiGe base profile will effectively have asmaller band gap in the strained SiGe base offering a lower barrier forelectron injection into the base and importantly, maintaining a lowerbase resistance and shorter transit time with the use of a thinner andhighly doped boron doped SiGe base structure. However, such a thinheavily doped SiGe layered structure is very susceptible to dopantout-diffusion or re-distribution due to high concentration gradientsduring thermal treatments in the manufacturing process. In fact, one ofthe key problems in the present SiGe npn BiCMOS technology of one majormanufacturer is to retain the narrow as-grown boron profile within theSiGe base layer and eliminate the undesirable out-diffusion of boronfrom the base region caused by heat treatments or transient enhanceddiffusion (TED) from post-epitaxial processing of annealing implantationdamages and CMOS integrations. Unfortunately, out diffusion of borondoes present a severe problem since it limits the final achievablebase-width in the base of the bipolar transistor regardless of hownarrow the base-width may have been originally generated. Moreover, incases where the boron diffuses or extends outside of the SiGe baseregion this can cause undesirable conduction band barriers to be formedat the base-collector junction which will degrade the collector currentand subsequently the high frequency performance of the bipolar device.

The classic solution to this problem has been to accommodate theout-diffusion of boron rather than to resolve it, i.e. is to grow anextended undoped spacer of SiGe on either side of the doped base regionbetween the emitter and collector regions. However, in such a case thetechnological problem then reverts back to minimizing and adjusting thethickness of the SiGe spacer layers in order to avoid strain-induceddefect formation within the SiGe base structure. Moreover, even then,the thicknesses of the undoped spacer layers selected to alleviate oraccommodate the out-diffusion problem is still restricted and limited bycritical thickness considerations and there may not be suitable spacerlayers to accommodate the out-diffusion of boron problem. The idealsolution to prevent or reduce the boron base dopant out-diffusion fromoccurring is a well known chemical effect that the presence or additionof carbon in a boron doped Si or SiGe layer can significantly reduce theout-diffusion of boron from the initial as-grown dopant profile.Moreover, H. J. Osten et, al., in the paper entitled “Carbon Doped SiGeHeterojunction Bipolar Transistors for High Frequency Applications”,IEEE BCTM 7.1, 1999, pp 109-116, which is incorporated herein byreference, have recently shown that low carbon concentration (<10²⁰atom·cm⁻³) can significantly suppress boron out-diffusion withoutaffecting the strain or band alignment and successful applications ofcarbon-rich layers for SiGe heterojunction bipolar transistors.Nevertheless, there exist a number of difficult material issues andproblems associated with the growth of device quality SiC or SiGeCfilms. First, carbon has a very low equilibrium solid solubility in Sithat is approximately 3.5×10¹⁷ atoms·cm⁻³ (<10⁻³ atomic %) at itsmelting point and it is even lower at the typical growth temperatures<1000 C. Second, the presence of carbon contamination on a Si surface isknow to disrupt the epitaxial growth and finally, there is a tendency toprecipitate silicon carbide (beta-SiC) at high growth or annealingtemperatures. Therefore, the biggest material problem is the ability togrow device quality Si:C and SiGe:C films at low temperatures,especially for the UHV-CVD process which is a fully manufacturableprocess currently being used in IBM's BiCMOS technology.

A prior technique of UHV-CVD for depositing and fabricating very thinepitaxial layers having abrupt transitions in dopant concentrationbetween adjacent single crystal layers at low temperatures is describedin U.S. Pat. No. 5,906,680 which issued on May 25, 1999 to B. S.Meyerson entitled “Method and Apparatus for Low Temperature, LowPressure Chemical Vapor Deposition of Epitaxial Silicon Layers” andassigned to the assignee herein. In U.S. Pat. No. 5,906,680 an apparatusis described where the characteristic of the growth system is providedto have an ultrahigh vacuum integrity in the range of about 10⁻⁹ Torrprior to epitaxial deposition at temperatures of less than 800° C.Furthermore, the epitaxial silicon or silicon germanium layers can bedoped in-situ to provide very abrupt defined regions of either n- orp-type conductivity. However, a suitable method for depositingsilicon-carbon or silicon germanium-carbon by this technique has not yetbeen described.

The ability to grow and achieve high carbon concentrations in bothdevice quality Si and SiGe films at low temperatures (<550° C.) has notbeen demonstrated by any other growth techniques or processes suitablefor batch-size, manufacturing operations. There are, however, lowtemperature growth techniques such as molecular beam epitaxy (MBE),solid phase epitaxy regrowth and rapid thermal CVD (RT-CVD) which havebeen successfully employed to grow SiC and SiGeC layers with carbonlevels up to 1%-3% carbon but often the material quality is not suitablefor device applications.

SUMMARY OF THE INVENTION

In accordance with the present invention, an apparatus and process forachieving epitaxial silicon carbon and silicon germanium carbon filmswithout the above mentioned problems is described, and in particular amanufacturable technique for batch processing of multiple wafers for thegrowth of expitaxial silicon carbon or silicon germanium carbon filmsthereon is provided. Furthermore, the fabrication of very thin epitaxiallayers of silicon carbon or silicon germanium carbon having abrupttransitions of several atomic widths in carbon concentration betweenadjacent single crystal layers, which cannot be achieved by any priorart techniques, is provided. In the present invention, the temperaturesand pressures of the growth technique are much less than those utilizedin the prior art, and are such that the growth process is nonequilibriumin nature whereby the growth kinetics on the silicon containing surface,rather than the equilibrium thermodynamics of the inlet gases, dictatethe deposition process. A hot wall, isothermal CVD apparatus asdescribed in U.S. Pat. No. 5,906,680 is utilized whereby essentially nohomogeneous gas phase pyrolysis of the silicon and/or carbon precursorsuch as silane or ethylene source gas occurs during the residence time,which is less than 1 second, within the selected temperature regimewhere the growth process is operated. Similar to U.S. Pat. No. 5,906,680heterogeneous chemistry where kinetic reactions at the surface of thesubstrate occur by design of method and apparatus, are the primarydeterminants of epitiaxial deposition of silicon carbon and silicongermanium carbon films.

It is a primary object of the present invention to provide a method andapparatus for performing epitaxial single crystal deposition of siliconcarbon layers in a batch process.

It is a further object of the present invention to provide an apparatusand method for enabling low temperature epitaxy of silicon carbon layershaving very low concentrations of oxygen contaminants in the SiC layers,preferably less than 1×10¹⁷ O atoms cm⁻³.

It is a further object of the present invention to provide an apparatusand method for enabling low temperature epitaxy of silicon carbon layersin the temperature range from 475° C. to 850° C.

It is a further object of the present invention to provide a method andapparatus for performing epitaxial single crystal deposition of silicongermanium carbon layers in a batch process.

It is a further object of the present invention to provide an apparatusand method for enabling low temperature epitaxy of silicon germaniumcarbon layers having very low concentrations of oxygen contaminants inthe SiGeC layers, preferably less than 1×10¹⁷ O atoms cm⁻³.

It is a further object of the present invention to provide an apparatusand method for enabling low temperature epitaxy of silicon germaniumcarbon layers in the temperature range from 350° C. to 850° C.

It is a further object of the present invention to provide a method andapparatus for performing polycrystalline deposition of silicon carbonlayers in a batch process.

It is a further object of the present invention to provide an apparatusand method for enabling low temperature polycrystalline deposition ofsilicon carbon layers having very low concentrations of oxygencontaminants in the SiC layers, preferably less than 1×10¹⁷ O atomscm⁻³.

It is a further object of the present invention to provide an apparatusand method for enabling low temperature deposition of polycrystallinesilicon carbon layers in the temperature range from 475° C. to 1200° C.

It is a further object of the present invention to provide a method andapparatus for performing deposition of polycrystalline silicon germaniumcarbon layers in a batch process.

It is a further object of the present invention to provide an apparatusand method for enabling low temperature deposition of polycrystallinesilicon germanium carbon layers having very low concentrations of oxygencontaminants in the SiGeC layers, preferably less than 1×10¹⁷ O atomscm⁻³.

It is a further object of the present invention to provide an apparatusand method for enabling low temperature deposition of polycrystallinesilicon germanium carbon layers in the temperature range from 350° C. to1200° C.

It is a further object of the present invention to provide a method andapparatus for performing in-situ p- or n-type doping of epitaxial singlecrystal silicon carbon layers which can withstand furnace anneals totemperatures of 850° C. and rapid thermal anneal temperatures to 1000°C.

It is a further object of the present invention to provide a method andapparatus for performing in-situ p- or n-type doping of polycrystallinesilicon carbon layers which can withstand furnace anneals totemperatures of 850° C. and rapid thermal anneal temperatures to 1000°C.

It is a further object of the present invention to provide a method andapparatus for performing in-situ p- or n-type doping of epitaxial singlecrystal silicon germanium carbon layers which can withstand furnaceanneals to temperatures of 850° C. and rapid thermal anneal temperaturesto 1000° C.

It is a further object of the present invention to provide a method andapparatus for performing in-situ p- or n-type doping of polycrystallinesilicon germanium carbon layers which can withstand furnace anneals totemperatures of 850° C. and rapid thermal anneal temperatures to 1000°C.

BRIEF DESCRIPTION OF THE DRAWING

These and other features, objects, and advantages of the presentinvention will become apparent upon consideration of the followingdetailed description of the invention when read in conjunction with thedrawing in which:

FIG. 1 is a graph of carbon and germanium concentrations versus layerdepth as a function of the flow rates of ethylene gas with a constantflow rate of silane.

FIG. 2 is a cross section TEM of the layer structure associated with thecurves of FIG. 1.

FIG. 3 is a graph of carbon and germanium concentrations versus layerdepth as a function of the flow rates of germane with a constant flowrate of silane and ethylene.

FIG. 4 is a graph of carbon and germanium concentrations versus layerdepth as a function of flow rates of germane with a constant flow rateof silane and ethylene.

FIG. 5 is a cross section TEM of the layer structure associated with thecurves of FIG. 4.

FIG. 6 is a graph of carbon and germanium concentrations versus layerdepth as a function of flow rates of ethylene with a constant flow rateof silane and germane.

FIG. 7 is a graph of carbon concentration versus layer depth as afunction of ethylene and ethane flows at several depositiontemperatures.

FIG. 8 is a graph of carbon concentration versus layer depth as afunction of two mixtures of ethane at several deposition temperatures.

FIG. 9 is a graph of the carbon and oxygen concentrations in a siliconlayer grown after growing multiple layers of carbon doped silicon andcarbon doped silicon germanium such as shown in FIGS. 1, 3, 4 and 6.

FIG. 10 is a graph of germanium, carbon and boron concentrations in asilicon and/or silicon germanium layer as a function of depth.

FIG. 11 is a graph of the boron concentration in a silicon germaniumlayer as a function of depth after furnace anneal with the curve ofcarbon concentration as a function of depth prior to furnace annealreproduced from FIG. 10.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

This invention is an apparatus and process for depositing epitaxialsingle crystal silicon carbon and silicon germanium carbon layers of adesired thickness on a silicon containing substrate, and in particularto provide a process whereby single crystal silicon carbon alloy layerscan be epitaxially deposited on a multitude of substrates. These siliconcarbon and silicon germanium carbon alloy films are of highcrystallographic perfection suitable for device applications andfurthermore, can be in-situ doped to any desired levels without anyoxygen contamination which is detrimental to device performances. Thepresent invention of growing silicon carbon and silicon germanium carbonfilms, i.e. SiC, SiC:B, SiC:P, SiGeC, SiGeC:B, SiGeC:P utilizes theUHV-CVD technique for growing epitaxial Si and SiGe films on a siliconcontaining substrate. For a description of the UHV-CVD growth technique,reference is made to U.S. Pat. No. 5,298,452 which issued Mar. 29, 1994to B. S. Meyerson and to U.S. Pat. No. 5,906,680 which issued May 25,1999 to B. S. Meyerson which are incorporated herein by reference. AUHV-CVD reactor suitable for growing the above-mentioned silicon andsilicon germanium containing films is available from Unaxis, SwitzerlandEpigress, Sweden, and CVD Equipment Corp., Ronkonkoma, 1 New York, USA.

Referring to the drawing, FIG. 1 shows a graph of the carbonincorporation into silicon during epitaxial growth in a UHV-CVD system.In FIG. 1, the ordinate represents carbon concentration and the abscissarepresents depth below the top surface of the final layer. The carbonprecursor was ethylene at 2% by volume in a mixture of ethylene (C₂H₄)and helium. In FIG. 1, curve 12 represents carbon in the silicon layerand curve 14 represents germanium in the silicon layer. Theconcentrations of carbon and germanium were measured using a secondaryion mass spectrometry (SIMS) system. Before depositing this film theUHV-CVD system was pumped down to a base pressure below 10⁻⁸ Torr andpreferably about 5×10⁻⁹ Torr in the temperature range from 450° C. to500° C. The surface of the wafers were heated in the range from 475° C.to 850° C. Spacer layers of silicon germanium were grown between periodsof introducing carbon into the silicon. The growth temperature for thisexample was 500 C. and the growth pressure was 2-3 millitorr. Theresulting germanium spacer regions and silicon carbon layers are shownin FIG. 2 which is a photograph of a cross section TEM view.

The substrate 16 shown in FIG. 2 has an initial carbon concentrationshown by curve portion 18 in FIG. 1, which is determined by thebackground level of the SIMS characterization system. Curve peak 19 inFIG. 1 is the carbon concentration at the substrate surface 20 prior toforming a silicon layer thereover. The carbon at the surface is due tothe residual from the wafer cleaning process which is not removed in theUHV-CVD system due to the absence of a high temperature prebake.

First, a silicon germanium region or layer 22 is grown on surface 20where the germanium concentration is about 15 atomic % shown by curveportion 22. Next, the germanium precursor is turned off and the ethyleneis turned on at a flow of 3 sccm to form silicon carbon. Curve portion24 shows the concentration of carbon at 2.42×10²⁰ atoms/cm⁻³. Thecorresponding layer or region 24′ is shown in FIG. 2. The above sequenceis repeated to form silicon germanium regions 26, 30, 34, 38 and 42 andcarbon regions 28, 32, 36, 40 and 44. A silicon germanium surface cap 46was formed over carbon region 44. Layers 24, 28, 32 and 36 wereepitaxial while layers 40 and 44 had carbon concentrations high enoughto form polycrystalline regions. Silicon germanium layers 42 and 46which are grown on silicon carbon layers 40 and 44 also showspolycrystalline regions associated with layers 40 and 44. The peakcarbon concentration levels in regions 24, 28, 32 and 36 increaseslinearly with a linear increase in carbon precursor flow rate. Carbonregions 24, 28, 32, 36, 40 and 44 were grown at flow rates of ethyleneof 3, 6, 9, 15, 25, and 35 sccm, respectively. Peak carbonconcentrations of carbon regions 24, 28, 32, 36, 40 and 44 were2.42×10²⁰, 4.97×10²⁰, 8.07×10²⁰, 1.46×10²¹, 1.94×10²¹, and 2.0×10²¹atoms cm⁻³, respectively. Carbon regions 24, 28, 32, 36, 40 and 44 hasan oxygen concentration which is less than 1×10¹⁷ atoms cm⁻³ accordingto SIMS, or below the background level of the SIMS detection system. Thelow level of oxygen contamination is due to the low initial basepressure in the deposition reactor and the choice of a precursorsuitable for the heterogeneous growth process where the chemicalreaction occurs on the growth surface. Ethylene as a precursor may besupplied from sources having other hydrocarbon mixtures such as ethane,methane, propane, butane, etc. Background ethylene levels as low as 450PPM in hydrocarbon mixtures will function as a carbon precursor. In FIG.2, prime reference numbers show layers corresponding to the curveportions with the same reference numbers in FIG. 1.

FIG. 3 is a graph of carbon concentration versus layer depth as afunction of the flow rate of germane with a constant flow rate of silaneand ethylene during epitaxial growth in a UHV-CVD system at 500° C.Curve 50 represents carbon concentration and curve 52 representsgermanium concentration. In FIG. 3, the ordinate represents carbonconcentration and the abscissa represents depth below the final layersurface. The silane flow rate was 30 sccm and the ethylene flow rate was10 sccm for curve portions 54-58 and 30 sccm for curve portion 59. Theethylene concentration was 2% by volume of a mixture of ethylene andhelium. The flow rate of germane was 2.5, 5, 10, 15 and 15 SCCM forcurve portions 62-66, respectively. A cap silicon germanium layer isshow by curve 67. FIG. 3 shows that increasing the flow of germaneresults in an increase in growth rate and a decrease of carbonconcentration. The inverse incorporation effect of carbon and germaniumis similar to that of phosphorous and germanium which is furtherdescribed in “SiGe Technology: Heteroepitaxy and High-SpeedMicroelectronics”, by P. M. Mooney and J. O. Chu published as chapter 5,pages 335-362 of the book edited by Elton N. Kaufmann and published byAnnual Reviews in 2000. However, for layers 65 and 66 deposited atconstant germanium flow increasing the ethylene from 10 sccm to 30 sccmresults in linear increase the carbon concentration. In FIG. 3, spacerlayers 70-74 contained 5% germanium.

FIG. 4 is similar to FIG. 3 except that the mixture of ethylene waschanged from 2% by volume to 1% by volume of a mixture of ethylene andhelium. Curves and curve portions in FIG. 4 have reference numbers whichare prime with respect to the corresponding reference numbers in FIG. 3.In FIG. 4, the ordinate represents carbon concentration and the abscissarepresents depth below the final layer surface. The silane flow rate was30 sccm and the 1% ethylene flow rate was 20 sccm for curve portions54′-58′ and 60 sccm for curve portion 59′. The comparison of FIGS. 3 and4 shows that the inverse incorporation effect of carbon and germanium isindependent of concentration of the ethylene mixture. This effect isbelieved to be due to the poisoning effect of carbon similar to that ofphosphine which has an inverse relation to growth rate.

FIG. 5 is a photograph of a cross sectional TEM of the sample discussedin FIG. 4. In FIG. 5 like reference numbers with double primes are usedfor corresponding curves or curve portions of FIG. 4 with single primereference numbers. Layers 54″-59″ are silicon germanium layers thatinclude carbon incorporated during growth. Layers 54″-59″ are allepitaxial single crystal layers. Substrate 16′ which may be, forexample, silicon has an upper surface 20′.

FIG. 6 is a graph of carbon concentration versus layer depth as afunction of flow rates of 2 percent ethylene in a mixture of ethyleneand He and with a constant flow rate of silane and germane duringepitaxial growth in a UHV-CVD system at 500° C. Germanium regions 80-89,deposited at a constant Ge flow rate, show an increase of germaniumconcentration caused by the increase of the carbon concentration.Germanium region 80 has no carbon because it was grown in the absence ofethylene, 0 percent at 0 sccm. Carbon regions 91-99 overlay germaniumregions 81-89. Carbon regions 91-99 were deposited at ethylene flow ratefrom 5 to 45 sccm in increments of 5 sccm, respectively. Spacer regions101-108 were formed between carbon regions 91-99 by turning off theethylene flow and reducing the germane flow rate. Carbon region 98 isstarting to form polycrystalline material due to the high carbonconcentration of about 1×10²⁰ atoms cm⁻³. Carbon region 99 has a peakconcentration of about 2×10²⁰ atoms cm⁻³. Carbon region 99 causes adecrease in the germanium concentration as shown by curve 98 and formspolycrystalline regions.

FIG. 7 is a graph of carbon concentration versus layer depth as afunction of flow rates of ethylene and ethane with a constant flow rateof silane during epitaxial growth in a UHV-CVD system at severaldeposition temperatures. In FIG. 7, the ordinate represents carbonconcentration and the abscissa represents depth below the top surface.Curve 116 shows the carbon concentration in the film as a function ofdepth. Curve portion 118 shows the background carbon concentration whichis similar to curve portion 18″ in FIG. 6. Curve portion 119 shows thebackground carbon concentration at the initial substrate surface priorto forming a silicon layer thereover. Curve portion 120 shows silicongrowth without carbon. Curve portion 122 shows carbon doped silicongrowth where the growth conditions are: UHV-CVD and substratetemperature 500° C., silane flow rate equals 30 sccm, ethane flow rateequals 50 sccm where ethane is 10% of a mixture of ethane and helium,the mixture also includes a background content of 450 ppm ethylene andthe pressure is about 2-3 millitorr. The 10 percent mixture of ethanehas a purity level of ethane of 99 percent. This low amount of ethyleneis still enough to enable carbon to be incorporated into the growingsilicon layer. The ethane and 450 ppm ethylene is turned off which isshown in curve portion 124. Curve portion 126 shows the same silane flowbut the ethylene is turned on at a flow rate of 3 sccm of 100% ethylene.The 100 percent mixture of ethylene has a purity level of ethylene of99.95 percent. Curve portion 128 shows the carbon concentration wherethe ethylene is turned off. Curve portion 130 shows where ethylene isturned on with a flow rate of 5 sccm of 100% ethylene. Curve portions130 and 126 show a peak carbon concentration of 7×10²¹ atoms cm⁻³. Curveportion 122 shows a peak carbon concentration of about 1×10²⁰ atomscm⁻³. Even small concentrations such as 450 ppm can function toincorporate carbon into the silicon film showing that ethylene is theactive precursor for incorporating carbon.

In Curve portion 132 the ethylene is turned off and at reference line133, the temperature is increased from 500° C. to 525° C. Afterreference line 133, the growth conditions beginning with curve portion122 are repeated as shown by curve portions 122′ to 130′ at 525° C. Atreference line 135, the temperature is increased from 525° C. to 550° C.After reference line 135, the growth conditions beginning with curveportion 122 are repeated as shown by curve portions 122″ to 130″ at 550°C. Regardless of the temperature, the small concentrations of ethyleneassociated with the ethane mixture still shows carbon incorporationindicating that ethylene is the active precursor.

FIG. 8 is a graph of carbon concentration versus layer depth as afunction of 10% and 50% concentration of ethane in helium at severaldeposition temperatures. The 10% mixture has a purity level of ethane of99% and the 50% mixture has a purity level of ethane of 99.95%. In FIG.8, the ordinate represents carbon concentration and the abscissarepresents depth below the top surface. Curve 116′ shows the carbonconcentration in the film as a function of depth. Curve portion 118′shows the background carbon concentration which is similar to curveportion 118 in FIG. 7 and curve 18″ in FIG. 6. Curve portion 119′ showsthe background carbon concentration at the initial substrate surfaceprior to forming a silicon layer thereover. Curve portion 120′represents silicon growth without carbon. Curve portion 142 shows carbondoped silicon growth where the growth conditions are: UHV-CVD chamberand substrate temperature 500° C., silane flow rate equals 30 sccm,ethane flow rate equals 50 sccm where ethane is 10% of a mixture ofethane and helium, the mixture also includes a background content of 450ppm ethylene and the pressure is about 2-3 millitorr. This low amount ofethylene is still enough to enable carbon to be incorporated into thegrowing silicon layer. The ethane and ethylene is turned off which isshown in curve portion 144. Curve portion 146 shows the same silane flowbut the ethane is turned on at a flow rate of 50 sccm of 50% ethane in amixture of ethane and helium. Curve portion 148 shows the carbonconcentration where the ethane is turned off. Curve portion 150′ showswhere ethane is turned on with a flow rate of 90 sccm of 50% ethane in amixture of ethane and helium. Curve portion 150 shows a peak carbonconcentration of 6×10¹⁸ atoms cm⁻³. Curve portion 146 shows a peakcarbon concentration of 4.5×10¹⁸ atoms cm⁻³. Curve portion 142 shows apeak carbon concentration of about 7×10¹⁹ atoms cm⁻³. Curve 146 and 150result from the 50% ethane concentration while curve 142 results fromthe 10% ethane concentration. If ethane was a contributing agent to thecarbon incorporation, then one would expect curves 146 and 150 to behigher than curve 142. FIG. 8 shows that ethane is not a precursor forcarbon incorporation even though it provides a lot of carbon in the gas.Even small concentrations of ethylene such as 450 ppm can function toincorporate carbon into the silicon film showing that ethylene is theactive precursor for incorporating carbon. A gas analysis of 10% ethaneshowed 450 ppm of ethylene as background gas or contaminate.

In curve portion 152, the ethane is turned off and at reference line153, the temperature is increased from 500° C. to 525° C. Afterreference line 153, the growth conditions beginning with curve portion142′ are repeated as shown by curve portions 142′, 144′, 146′, 148′,150′ and 152′ at 525 C. At reference line 155, the temperature isincreased from 525° C. to 550° C. After reference line 155, the growthconditions beginning with curve portion 142′ are repeated as shown bycurve portions 142″, 144″, 146″, 148″, 150″ and 152″ at 550° C.Regardless of the temperature, the concentrations of 50% ethaneassociated with the ethane mixture still shows less carbon incorporationthan the 10% ethane indicating that ethylene (450 ppm in the 10% ethaneas measured) is the active precursor.

FIG. 9 is a graph of the carbon and oxygen concentrations in a siliconlayer grown after growing multiple layers of carbon doped silicon andcarbon doped silicon germanium such as shown in FIGS. 1, 3, 4 and 6. Thecarbon source used in FIGS. 1, 3, 4 and 6 was ethylene. In FIG. 9, theleft ordinate represents concentration and the abscissa represents depthof the film below the top surface. The right ordinate representssecondary ion counts. Curve 160 shows the oxygen concentration as afunction of depth. A silicon substrate has an upper surface at about 0.2microns depth as shown by reference line 162. Curve portion 164represents the ambient oxygen concentration in the substrate which is1×10¹⁸ atoms cm−3. Curve portion 166 represents the oxygen at thesilicon substrate interface formed by an epitaxial silicon layer grownon the substrate. The peak oxygen of curve portion 166 was 1×10¹⁹ atomscm−3. Curve portion 168 shows the oxygen concentration in the siliconlayer which is about 1×10¹⁸ atoms cm−3. Curve portion 169 shows anapparent increase of oxygen concentration near the silicon layer surfacedue to the presence of a native oxide. The SIMS tool uses a Cs+ as thesputtering beam.

Curve 170 shows the carbon concentration as a function of depth. Curveportion 174 represents the ambient carbon concentration in the substratewhich is 2×10¹⁷ atoms cm−3. Curve portion 176 represents the carbon atthe silicon substrate interface formed by an epitaxial silicon layergrown on the substrate. The peak carbon concentration of curve portion166 was 5×10¹⁸ atoms cm−3. Curve portion 178 shows the carbonconcentration in the silicon layer which is about 3×10¹⁷ atoms cm−3.Curve portion 179 shows an apparent increase of carbon concentrationnear the silicon layer surface due to the presence of contaminants fromthe chamber ambient and residuals from the wafer cleaning process. TheSIMS tool uses a Cs+ beam as the sputtering source.

FIG. 9 shows that there is no further oxygen or carbon contaminationsfrom the earlier use of the ethylene precursor or any associatedmixtures of ethylene. The UHV-CVD chamber remains operational (having nobackground carbon and a base pressure of less than 10⁻⁹ Torr.) withrespect to the background contaminates to enable further growth ofepitaxial silicon or silicon germanium layers as described in U.S. Pat.No. 5,298,452 by Meyerson which issued Mar. 29, 1994. Carbon may beincorporated into silicon layers or silicon germanium only due to theethylene precursor gas and where no carbon incorporates into the layerfrom the background. When the flow of the ethylene precursor gas isturned off, there is no carbon or oxygen memory effect i.e. no continuedincorporation of carbon.

The fact that there is no memory effect, is substantiated by thelaboratory data given in Table 1. Table 1 provides data via SIMSmeasurements taken from 14 samples.

TABLE 1 C and O Baselines for Hex Tool 349, Mostly March–May 2000Referenced to standard “II” which is similar to YKT Interface InterfaceC/cm3 Date 3/00 C/O C/cm2 O/cm2 in epi January 2000 PR952-12 3.9E121.9E12 1.1E17 Run21431E72-UMCA revisit March 2002 CP1057-Run247 2.7E126.0E11 — UHVA March 2002 CP1057-Run255 2.6E12 1.9E12 1.1E17 SSDA March2002 CP1057-Run258 5.5E12 1.1E13 1.4E17 March 2002 CP1057-Run262 1.4E132.4E13 1.4E17 SSOA Mar. 31, 2000 CP1126-Run302 6.0E12 1.1E13 1.5E17Slot5 After Recovery Mar. 31, 2000 CP1126 Run302 6.0E12 7.6E12 1.5E17Slot8 after recovery 4/4 CP1135 Run310 3.0E12 1.3E12 1.1E17 Slot8 FILTERIN PLACE, Ethylene run 4/24 CP1178-2 Run 324   3E12   4E12 1.0E17 afterethylene runs 5/2 CP1197-Run333 5.4E12 1.2E13 1.5E17 Control Run afterethylene runs 5/14 CP1232 run after 5.4E12   9E12 1.2E17 ethylene runs6/8 CP 1314 - Run 376   1e13 1.2e13 1.4e17 after ethylene run CP-1314Run 378? 1.5E13 1.9E13 1.4E17 6/15 CP 13124 - Run 1.4E13 2.0E13 1.3E17380 after the ethylene run

In the first column of Table 1, 14 different days over six months wereused for growing a silicon film on a substrate similar to the siliconlayer grown on a substrate as described in FIG. 9. Column 2 gives ashort description of the sample name and sample number run. The sampleswere run in a common tool, Sirus manufactured by Leybold now Unaxis.Column 3 shows data of carbon at the silicon layer interfacecorresponding to curve portion 176 in FIG. 9. Column 4 shows data ofoxygen at the silicon layer interface corresponding to curve portion 166in FIG. 9. Column 5 shows data of the carbon concentration in thesilicon containing layer corresponding to curve portion 178. The data incolumns 3-5 are within acceptable ranges or criteria for growingepitaxial silicon containing layers by UHV-CVD.

FIG. 10 is a graph of SIMS data as a function of depth taken fromsilicon containing layers grown by UHV CVD with various concentrationsof germanium, carbon and boron incorporated therein. The growth of thelayers were formed in a continuous process without interruption orbreaking vacuum. The growth conditions were at 550 C. The word “layer”as used is a general term to denote a region of growth with aconcentration above and/or below a predetermined value. In FIG. 10, theleft ordinate represents respective carbon or boron concentration inatom/cc and the right ordinate represents germanium concentration inatomic percent. The abscissa represents depth in microns below the topsurface of the final layer. An initial silicon substrate was used forgrowing epitaxial silicon containing layers thereon. The siliconsubstrate had a top surface which is now at a depth of about 0.79microns shown by reference line 180 in FIG. 10.

In FIG. 10, the germanium concentration is shown by curve 182, the boronconcentration is shown by curve 184; and the carbon concentration isshown by curve 186. At the interface of the silicon substrate and thesilicon containing layer an increase in carbon is shown by curve portion188 and an increase of boron is shown by curve portion 190. First on theupper surface of the substrate, a layer of silicon with germanium wasgrown with a germanium concentration of about 9 atomic percent as shownby curve region 192. In the layer of curve region 192, the concentrationof boron and carbon was due to background contamination. Next, the Geprecursor was turned off as shown by curve portion 194 where the Geconcentration decreased to about 4 atomic percent. The Ge precursor wasturned on again to provide curve portion 196 with a Ge concentration ofabout 8.2 percent. In the middle of curve portion 196, the boronprecursor was turned on to provide a peak in B of about 4.5×10¹⁹atoms/cc shown by curve portion 198. It is noted that the carbonconcentration remained the same and that a layer of SiGeB had beenformed with the Ge concentration at about 8.2 percent. The B precursorwas turned off as shown by curve portion 199 and then the Ge precursorgas was turned off as shown by curve portion 200.

A substantially Si layer was grown at curve portion 202 where the Geconcentration was about 4 percent. The Ge precursor was turned on againas shown by curve portion 204. In the middle of curve portion 204, theboron precursor and the carbon precursor gases were tuned on as shown byrespective curve portions 206 and 208. The carbon precursor gas wasC₂H₄. The boron precursor and the carbon precursor gases were thenturned off. Thus a SiGeB:C layer was grown at the depth of curveportions 206 and 208. Then the Ge precursor gas was turned off as shownby curve portion 210 where a substantially silicon layer was grown witha Ge concentration of about 4 atomic percent. The Ge precursor gas wasturned on again as shown by curve portion 212 and then turned off again.At the top surface, the carbon concentration and boron concentrationincreased due to contamination. In summary, FIG. 10 shows two buriedSiGe layers in silicon at the depths of curve portions 192 and 212, aSiGeB layer without C at the depth of curve portion 198 with a SiGelayer on both sides and a SiGeB:C layer at the depth of curve portions206 and 208 with a SiGe layer on both sides.

FIG. 11 shows the results of SIMS measurements of boron after the samplehaving the concentration profiles of FIG. 10 is subject to a furnaceanneal at 850° C. for 30 minutes. In FIG. 11, the ordinate on the lefthand side represents Boron concentration in atoms/cc. The abscissarepresents depth below the surface in microns. In FIG. 11, the ordinateand abscissa are the same as the left ordinate and abscissa respectivelyin FIG. 10. Curve 184 from FIG. 10 is reproduced in FIG. 11. Curve 220shows the boron concentration profile of the sample measured after thefurnace anneal at 850° C. for 30 minutes. Curve portion 222 has about2.4 times the width at 10×10¹⁸ atoms/cc as curve portion 198 as shown byarrow 224. Curve portion 226 has about 1.35 times the width at 10×10¹⁸atoms/cc as curve portion 206 as shown by arrow 228. The presence ofcarbon at the same depth as curve portion 206 where the carbon was about0.05 percent (2.5×10¹⁹ atoms/cc) is believed to block the boron fromdiffusing during furnace anneal at 850° C. for 30 minutes. The carbon isbelieved to occupy the substitutional sites in the silicon germaniumcrystal lattice and thus block boron from diffusing by way ofsubstitutional sites. As shown in FIG. 11, there is a measurabledifference in the out-diffusion of boron in SiGe with C present (0.05percent) as compared to the out-diffusion of boron in SiGe where C isnot present (0.00 percent). Preservation, of the original grown Bprofile in Si and SiGe layers is important to obtain superior devicestructures such as FET and bipolar transistors.

U.S. patent application Ser. No. 09/774126 filed Jan. 30, 2001 by Chu etal. entitled “Incorporation of Carbon in Silicon/Silicon Germaniumepitaxial layer to Enhance Yield for Si—Ge bipolar technology” referredto above is directed to a method of fabricating a SiGe bipolartransistor including carbon in the collector region as well as the SiGebase region and is assigned to the assignee herein and incorporatedherein by reference.

While there has been described and illustrated a method and structurefor incorporating carbon into silicon and silicon germanium layers withor without in-situ doping and with abrupt concentration profiles andwith low levels of oxygen, it will be apparent to those skilled in theart that modifications and variations are possible without deviatingfrom the broad scope of the invention which shall be limited solely bythe scope of the claims appended hereto.

1. A layered structure comprising: a substrate having an upper surfaceof single crystalline Si, and a multitude of single crystal layers ofmaterials selected from the group consisting of Si, SiGe, SiC, and SiGeCover said upper surface, said Si/SiC, Si/SiGeC, SiGe/SiC and SiGe/SiGeClayer interfaces having an abrupt change in C concentration above 1×10¹⁸atoms/cc over a layer thickness in the range from about 6 Angstroms toabout 60 Angstrom, wherein the oxygen in said carbon containing layer isless than 1×10¹⁷ atoms/cc, and with the proviso that when said carboncontaining layers include a p-type dopant, said p-type dopant is in therange from about 1×10¹⁸ to about 1×10²¹ atoms/cc and wherein said p-typedopant profile can withstand furnace anneals to temperatures of 850° C.and rapid thermal anneal temperatures to 1000° C., or when said saidcarbon containing layers include a n-type dopant, the n-type dopant isin the range from about 1 ×10¹⁸ to about 1×10²¹ atoms/cc.